The new cultivar ‘Willamette Thornless Marion’ is a thornless (spineless) naturally occurring mutation of the cultivar ‘Marion’ (non-patented). This new cultivar was discovered as a single primocane cane mutation of a ‘Marion’ blackberry plant growing in 2005 in a twenty acre field of cultivated ‘Marion’ plants in Clackamas County, Oreg.
The mutation grew as a single primocane from an established ‘Marion’ plant. The mutant primocane was observed during the routine hand wrapping of the ‘Marion’ primocanes on the trellis. New plants were asexually reproduced by tip layering the discovered mutant primocane; micro propagated plants have also been started from the mutant primocane. Both types produce true to type stable plants through successive generations.
The nearest and closest cultivar to the ‘Willamette Thornless Marion’ is the ‘Marion’. We use the ‘Marion’ for comparison as this new cultivar is a mutation of a ‘Marion’. The ‘Marion’ is a trailing blackberry commercially grown primarily in Oregon. The ‘Marion’ is widely produced and accounts for more than half of the blackberry production in Oregon. Virtually all blackberries use the ‘Marion’ (non-patented) as the base of comparison for vigor, color, flavor, production, cold hardiness and all other facets of a blackberry plant either commercially in use or in the development stage.
The main difference between the new cultivar and ‘Marion’ is that the new cultivar is substantially spineless. The normal term for spine or spineless, in the blackberry industry, is thorn or thornless). The new cultivar has fine and very few thorns whereas the ‘Marion’ has hardy thorns throughout the plant. One primary drawback with the ‘Marion’ is that the stems and petioles, which remain from the first year, have many thorns. The leaflets and leaves do fall off the ‘Marion’ primocanes during the dormant season; however most stems and petioles remain attached to the primocane. During mechanical harvest, these ‘Marion’ stems and petioles fall off and attach themselves to the fruit and they then become very difficult to remove. These ‘Marion’ stems and petioles with thorns then become a problem for producers, processors, and consumers. In contrast, the new cultivar has no spines/thorns on the stems or petioles. In so far as they have been observed, the other aspects of both the new cultivar and the ‘Marion’ are almost exactly the same with non-significant variations which exist in both cultivars.